Substrate for liquid crystal display and liquid crystal display having the same

ABSTRACT

A substrate for a transflective liquid crystal display that is capable of display in both reflective and transmissive modes and a display having the same. One embodiment includes a substrate that sandwiches a liquid crystal in combination with an opposite substrate formed with a common electrode on the opposing surface, a plurality of bus lines on a top surface of the substrate that intersect each other with an insulation film interposed therebetween, and thin film transistors formed near the intersections of the plurality of bus lines. A plurality of pixel regions constituted of a plurality of reflective regions in which reflective electrodes for reflecting incident light from the side of the top surface of the substrate are formed in a matrix and transmissive regions which are provided around the reflective regions and which transmit incident light from the side of a bottom surface toward the top surface of the substrate.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a substrate for a transflective liquidcrystal display that is used as a display of a portable electronicapparatus and that is capable of display in both of reflective andtransmissive modes and to a liquid crystal display having the same.

2. Description of the Related Art

Liquid crystal displays are generally categorized into transmissivetypes in which a transparent electrode constituted of an ITO (indium tinoxide) is formed at each pixel and which have a backlight unit on abackside thereof and reflective types in which a reflective electrodemade of aluminum (Al) is formed at each pixel. Among recent activematrix liquid crystal displays, reflective liquid crystal displays aredrawing attention for their lighter weights, low profiles, and low powerconsumption. Single polarizer type reflective liquid crystal displaysutilizing the TN (Twisted Nematic) mode as disclosed in Japanese PatentLaid-open No. 232465/1993 and Japanese Patent Laid-Open No. 338993/1996have already been put in use. However, the visibility of a reflectiveliquid crystal display is greatly dependent on the brightness of theambience, and a problem arises in that visibility is significantlyreduced in a dark place where ambient brightness is relatively low.

A transmissive liquid crystal display exhibits a high contrast ratio andhigh visibility even in a dark place because it is illuminated from thebackside thereof with a backlight unit. However, it has a problem inthat visibility is significantly reduced in a place where ambientbrightness is relatively high such as the outdoor in good weather (abright place). Further, since a backlight unit is always used, anotherproblem arises in that power consumption is great.

Liquid crystal displays that solve the above-described problems includefront light type reflective liquid crystal displays having a front lightunit that provides illumination from the side of the display screenthereof. However, a front light type reflective liquid crystal displayexhibits a contrast ratio lower than that of a transmissive liquidcrystal display in a dark place because illumination light from thefront light unit is reflected by not only the reflective electrodes butalso the surface of the display screen. In a bright place, it presentsdarker display in a bright place compared to a normal reflective liquidcrystal display because of light absorption at a light guide plate ofthe front light unit.

Another approach involves a transflective liquid crystal display inwhich transflective reflecting films are used as pixel electrodes asdisclosed in Japanese Patent Laid-Open No. 333598/1995. In general,metal thin films such as aluminum having a thickness of about 30 nm areused as the transflective reflecting films. However, this results in areduction in utilization of light because the metal thin films have ahigh absorption constant. Further, since it is difficult to formtransflective reflecting films having a uniform thickness in the planeof a substrate, there will be variations of light transmittance andreflectance in the plane of the substrate.

A transflective liquid crystal display that solves the above-describedproblems was disclosed in Japanese Patent Laid-Open No. 281972/1999.FIG. 29 shows a configuration of a transflective liquid crystal displayaccording to the related art. As shown in FIG. 29, a plurality of gatebus lines 104 extending in the vertical direction in the figure areformed in parallel with each other on a TFT substrate 102. A pluralityof drain bus lines 106 extending in the horizontal direction in thefigure are formed in parallel with each other such that they intersectwith the gate bus lines 104 with an insulation film which is not showninterposed therebetween. TFTs 108 are formed in the vicinity of thepositions where the bus lines 104 and 106 intersect with each other.Drain electrodes 140 of the TFTs 108 are electrically connected to thedrain bus lines 106. Source electrodes 142 are electrically connected toreflective electrodes 110 made of aluminum through contact holes 144.The regions where the reflective electrodes 110 are formed serve asreflective regions of respective pixels. Openings are provided in themiddle of the reflective electrodes 110 to form transparent electrodes112 made of ITO. The regions where the transparent electrodes 112 areformed serve as transmissive regions of respective pixels.

FIG. 30 is a sectional view of the liquid crystal display taken alongthe line X-X in FIG. 29. As shown in FIG. 30, the liquid crystal displayis constituted of the TFT substrate 102, an opposite substrate 114, anda liquid crystal layer 116 provided between the substrates 102 and 114.The TFT substrate 102 has a planarization film 120 in reflective regionson a glass substrate 118. A plurality of recesses and projections areformed on a surface of the planarization film 120. Reflective electrodes110 are formed on the planarization film 120. On a surface of thereflective electrodes 110, there are formed recesses and projectionswhich are associated with the recesses and projections formed on thesurface of the planarization film 120 located under the same. Thereflective electrodes 110 have improved light scattering characteristicsthanks to the plurality of recesses and projections on the surfacethereof, and they reflect and scatter external light incident thereuponin various directions.

Transparent electrodes 112 are formed in transmissive regions on theglass substrate 118. The transparent electrodes 112 transmit lightemitted by a backlight unit (not shown) provided under the same in thefigure. The transparent electrodes 112 are electrically connected to thereflective electrodes 110 through barrier metal layers 136 made oftitanium (Ti) or molybdenum (Mo).

The counter substrate 114 has a common electrode 130 that extendsthroughout a top surface of the glass substrate 119. Polarizers 132 and134 are applied to surfaces of the substrates 102 and 114 counter tosurfaces thereof facing each other, respectively.

The liquid crystal display shown in FIGS. 29 and 30 achieves display inboth of the reflective and transmissive modes by forming a reflectiveregion and a transmissive region at each pixel.

In the above-described configuration, however, it is necessary to formboth of the reflective electrodes 110 made of Al and the transparentelectrodes 112 made of ITO. Further, since corrosion attributable to abattery effect occurs when Al and ITO are formed in contact with eachother, the barrier metal layers 136 must be formed between thereflective electrodes 110 and the transparent electrodes 112. This hasresulted in a problem in that the liquid crystal display involvescomplicated manufacturing steps and in that an increase in manufacturingcost occurs.

In the above-described configuration, a reflective region and atransmissive region are formed at each pixel. Therefore, the displayexhibits reflection characteristics lower than those of a reflectiveliquid crystal display and transmission characteristics lower than thoseof a transmissive liquid crystal display. However, when the area of thereflective regions is increased to achieve improved reflectioncharacteristics, the area of the transmissive regions further decreasesto degrade the transmission characteristics further. Similarly, when thearea of the transmissive regions is increased to achieve improvedtransmission characteristics, the area of the reflective regionsdecreases to degrade the reflection characteristics further. Thus, in atransflective liquid crystal display in the related art, reflectioncharacteristics and transmission characteristics are in the relationshipof tradeoff, and a problem has arisen in that it is difficult to improveboth of the reflection characteristics and the transmissioncharacteristics.

Further, while light incident upon the reflective regions pass through acolor filter (CF) layer twice, the light passes through the CF layeronly once in the transmissive regions. This results in a chromaticdeviation between display in the reflective mode and display in thetransmissive mode. While a chromatic deviation can be opticallycompensated to some degree, it can degrade display characteristics.

SUMMARY OF THE INVENTION

The invention provides a substrate for a liquid crystal display thatprovides high display characteristics at a low cost and a liquid crystaldisplay having the same.

According to the invention, there is provided a substrate for a liquidcrystal display, characterized in that it has a substrate thatsandwiches a liquid crystal in combination with an opposite substrateprovided opposite thereto, a plurality of bus lines formed on a topsurface of the substrate such that they intersect with each other withan insulation film interposed therebetween, thin film transistors formedin the vicinity of positions where the plurality of bus lines intersectwith each other, and a pixel region constituted of a plurality ofreflective regions in which reflective electrodes for reflectingincident light from the side of the top surface of the substrate areformed in the form of a matrix and transmissive regions which areprovided around the plurality of reflective regions and which transmitincident light from the side of a bottom surface of the substrate towardthe top surface of the substrate.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing a liquid crystal display according to afirst basic configuration in a first mode for carrying out theinvention;

FIG. 2 is a diagram showing the liquid crystal display according to thefirst basic configuration in the first mode for carrying out theinvention;

FIG. 3 is a diagram showing a liquid crystal display according to asecond basic configuration in the first mode for carrying out theinvention;

FIG. 4 is a diagram showing a liquid crystal display having acombination of the first and second basic configurations in the firstmode for carrying out the invention;

FIGS. 5A and 5B show microphotographs of states of display ofpredetermined images on the liquid crystal display according to a firstembodiment in the first mode for carrying out the invention.

FIGS. 6A and 6B show states of display of predetermined images on theliquid crystal display according to the first embodiment in the firstmode for carrying out the invention;

FIGS. 7A and 7B schematically show a sectional configuration of a liquidcrystal display according to a second embodiment in the first mode forcarrying out the invention;

FIG. 8 shows an arrangement of optical axes of the liquid crystaldisplay according to the second embodiment in the first mode forcarrying out the invention;

FIGS. 9A and 9B schematically show a sectional configuration of theliquid crystal display according to the second embodiment in the firstmode for carrying out the invention;

FIGS. 10A to 10D show states of display of the liquid crystal display ina reflective mode according to the second embodiment in the first modefor carrying out the invention;

FIGS. 11A to 11D show states of display of the liquid crystal display ina transmissive mode according to the second embodiment in the first modefor carrying out the invention;

FIG. 12 shows an arrangement of optical axes of a liquid crystal displayaccording to a third embodiment in the first mode for carrying out theinvention;

FIGS. 13A to 13D show states of display of the liquid crystal display inthe reflective mode according to the third embodiment in the first modefor carrying out the invention;

FIGS. 14A to 14D show states of display of the liquid crystal display inthe transmissive mode according to the third embodiment in the firstmode for carrying out the invention;

FIG. 15 shows an arrangement of optical axes of a liquid crystal displayaccording to a fourth embodiment in the first mode for carrying out theinvention;

FIGS. 16A to 16D show states of display of the liquid crystal display inthe reflective mode according to the fourth embodiment in the first modefor carrying out the invention;

FIGS. 17A to 17D show states of display of the liquid crystal display inthe transmissive mode according to the fourth embodiment in the firstmode for carrying out the invention;

FIG. 18 shows an arrangement of optical axes of a liquid crystal displayaccording to a fifth embodiment in the first mode for carrying out theinvention;

FIGS. 19A to 19D show states of display of the liquid crystal display inthe reflective mode according to the fifth embodiment in the first modefor carrying out the invention;

FIGS. 20A to 20D show states of display of the liquid crystal display inthe transmissive mode according to the fifth embodiment in the firstmode for carrying out the invention;

FIG. 21 shows a configuration of a liquid crystal display according to asixth embodiment in the first mode for carrying out the invention;

FIGS. 22A and 22B show a configuration of a substrate for a liquidcrystal display according to a seventh embodiment in the first mode forcarrying out the invention;

FIG. 23 is a graph showing a relationship between reflectivity andaverage inclinations that is a prerequisite for the seventh embodimentin the first mode for carrying out the invention;

FIG. 24 shows a configuration of a liquid crystal display according toan eighth embodiment in the first mode for carrying out the invention;

FIG. 25 shows a modification of the configuration of the liquid crystaldisplay according to the eighth embodiment in the first mode forcarrying out the invention;

FIG. 26 shows another modification of the configuration of the liquidcrystal display according to the eighth embodiment in the first mode forcarrying out the invention;

FIG. 27 shows a configuration of a liquid crystal display in a secondmode for carrying out the invention;

FIG. 28 shows a modification of the configuration of the liquid crystaldisplay in the first mode for carrying out the invention;

FIG. 29 shows a configuration of a transflective liquid crystal displayaccording to the related art; and

FIG. 30 is a sectional view showing the configuration of thetransflective liquid crystal display according to the related art.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Mode for Carrying Out theInvention

A description will now be made with reference to FIGS. 1 to 26 on asubstrate for a liquid crystal display and a liquid crystal displayhaving the same in a first mode for carrying out the invention. First, adescription will be made with reference to FIGS. 1 and 2 on a firstbasic configuration according to the invention that is a prerequisite ofthe present embodiment. FIG. 1 shows a liquid crystal display having thefirst basic configuration. As shown in FIG. 1, a plurality of gate buslines 10 (FIG. 1 shows only one of them) extending in the verticaldirection in the figure are formed in parallel with each other on a TFTsubstrate (base substrate) 2. A plurality of drain bus lines 12extending in the horizontal direction in the figure are formed inparallel with each other such that they intersect with the gate buslines 10 with an insulation film that is not shown interposedtherebetween. TFTs 14 are formed in the vicinity of the intersectionsbetween the bus lines 10 and 12. Drain electrodes 16 of the TFTs 14 areextracted from the drain bus lines 12 and are formed such that theirends are located on edges of active semiconductor layers formed ofamorphous silicon (a-Si) on the gate bus lines 10 and channel protectionfilms formed on the same on one side thereof (the layers and films areboth omitted in the figure).

Source electrodes 18 of the TFTs 14 are formed such that they arelocated on other edges of the active semiconductor layers and channelprotection films on another other side thereof. In such a configuration,the gate bus lines 10 located directly under the channel protectionfilms serve as gate electrodes of the TFTs 14. Reflective electrodes 20are formed above the intersections between the bus lines 10 and 12 andthe TFTs 14. The source electrodes 18 of the TFTs 14 are electricallyconnected to the reflective electrodes 20 through contact holes 22.

FIG. 2 shows a section of the liquid crystal display taken along theline A-A in FIG. 1. The liquid crystal display has a TFT substrate 2, acounter substrate 4, and a liquid crystal layer 24 located between thesubstrates 2 and 4. The TFT substrate 2 and the counter substrate 4 areprovided opposite to each other with a cell gap d1 interposedtherebetween. For example, the TFT substrate 2 has a planarization film28 having a thickness substantially equal to the cell gap d1 on a glasssubstrate 26. A plurality of recesses and projections are formed on asurface of the planarization film 28. Reflective electrodes 20 and 20′made of Al are formed at each pixel on the planarization film 28. On asurface of the reflective electrodes 20 and 20′, there are formedrecesses and projections which are associated with the recesses andprojections formed on the surface of the planarization film 28 locatedunder the same. The reflective electrodes 20 and 20′ have improved lightscattering characteristics thanks to the plurality of recesses andprojections formed on the surface of the same, and external lightincident upon the reflective electrodes 20 and 20′ is scattered andreflected in various directions. The reflective electrodes 20 and 20′are provided at an interval w+w′.

The opposite electrode 4 has a common electrode 30 constituted of an ITOthat covers a surface of a glass substrate 27 entirely. Predeterminedpolarizers 32 and 34 are applied to surfaces of the substrates 2 and 4opposite to surfaces thereof facing each other, respectively. Abacklight unit (not shown) is provided under the TFT substrate 2 in thefigure.

The regions where the reflective electrodes 20 are formed constitutereflective regions R that reflect external light incident thereupon.Similarly, the regions where the reflective electrodes 20′ are formedconstitute reflective regions R′. Regions where the reflectiveelectrodes 20 and 20′ are not formed constitute transmissive regions Tand T′ that transmit light emitted by the backlight unit. Thetransparent electrodes T are located within ranges where they are at adistance w (≅d1) or closer to edges of the reflective electrodes 20, andthe transparent electrodes T′ are located within ranges where they areat a distance w′ (≅d1) or closer to edges of the reflective electrodes20′. That is, a reflective region R constitutes one pixel in combinationwith a transmissive region T provided in the neighborhood of the same. Areflective region R′ constitutes one pixel in combination with atransmissive region T′ provided in the neighborhood of the same. Notransparent electrode 112 as shown in FIG. 30 is formed in thetransmissive regions T and T′.

FIG. 2 shows a state of a reflective electrode 20 in which apredetermined grayscale voltage is applied thereto. The broken lines inthe figure indicate an electric field between the reflective electrode20 and the common electrode 30. In the transmissive region T, an obliquefield is generated between the common electrode 30 and an edge of thereflective electrode 20 at an angle to a direction perpendicular to thesubstrate surface. Liquid crystal molecules in the transmissive region Tare driven by the oblique field substantially similarly to liquidcrystal molecules in the reflective region R. In the transmissive regionT′, an oblique field is generated between the common electrode 30 and anedge of the reflective electrode 20′. Liquid crystal molecules in thetransmissive region T′ are driven by the oblique field substantiallysimilarly to liquid crystal molecules in the reflective region R′.

The planarization film 28 is removed in the transmissive regions T andT′. A cell gap d2 between the transmissive regions T and T′ issubstantially twice the cell gap d1 between the reflective regions R andR′, because the thickness of the planarization film 28 is substantiallysimilar to the cell gap d1. Therefore, retardation (Δn·d) that occurs inthe liquid crystal layer 24 when liquid crystal molecules are aligned inparallel with the substrate surface is λ/4 in the reflective regions Rand R′, and it is doubled or λ/2 in the transmissive regions T and T′.

In the first basic configuration of the invention, the reflectiveelectrodes 20 are provided at the intersections between the bus lines 10and 12 and on the TFTs 14 to reduce the area of the bus lines 10 and 12exposed in the transmissive regions T and T′ significantly, whichincreases the area of the transmissive regions T and T′ withoutdecreasing the area of the reflective regions R and R′. That is, in thefirst basic configuration, bus line wiring regions that have not beenused as reflective regions nor as transmissive regions in atransflective liquid crystal display in the related art are used as thetransmissive regions T and T′. Therefore, transmission characteristicscan be improved without degrading reflection characteristics to improveutilization of light. Further, no transparent electrode 112 is formed inthe transmissive regions T and T′ in the first basic configuration.Therefore, steps for forming transparent electrodes 112 and formingbarrier metal layers 136 can be omitted to reduce the manufacturingcost.

A second basic configuration of the invention will now be described withreference to FIG. 3. FIG. 3 shows a liquid crystal display having thesecond basic configuration. Components having functions and effects likethose in the liquid crystal display having the first basic configurationshown in FIG. 1 are indicated by like reference numerals and will not bedescribed. As shown in FIG. 3, reflective electrodes 20 a to 20 econstituting reflective regions R are formed in regions defined by gatebus lines 10 and drain bus lines 12. The reflective electrodes 20 a to20 e have openings 36 a to 36 e that are formed in variousconfigurations such as slits and circular and polygonal holes.

For example, the reflective electrode 20 a is formed with an opening 36a which is constituted of one slit extending in parallel with longersides of the reflective electrode 20 a and a plurality of slitsextending at an angle to the longer sides of the reflective electrodes20 a. The reflective electrode 20 b is formed with a plurality ofstraight openings 36 b extending in parallel with shorter sides of thereflective electrode 20 b. The reflective electrode 20 c is formed witha plurality of elongate rhombic openings 36 c extending in parallel withshorter sides of the reflective electrode 20 c. The reflective electrode20 d is formed with a plurality of circular openings 36 d. Thereflective electrode 20 e is formed with a plurality of wedge-shapedopenings 36 e extending in parallel with longer sides of the reflectiveelectrode 20 e.

The regions where the openings 36 a to 36 e are formed serve astransmissive regions T. No transparent electrode 112 as shown in FIG. 30is formed at the openings 36 a to 36 e. Liquid crystal molecules in thetransmissive regions T are driven by an oblique field between edges ofthe reflective electrodes 20 a to 20 e and a common electrode 30 (notshown in FIG. 3) substantially similarly to liquid crystal molecules inreflective regions R.

The openings 36 a to 36 e in each pixel may have the same configuration.The openings 36 a to 36 e may have a configuration to regulate alignmentof liquid crystal molecules. As a result, in a VA (Vertical Aligned)mode liquid crystal display in which liquid crystal molecules arealigned substantially perpendicularly to the substrate surface, separatealignments can be achieved without a process of rubbing the alignmentfilm. The present basic configuration may be used in a liquid crystaldisplay in the TN mode utilizing a horizontal alignment film or the HAN(Hybrid Aligned Nematic) mode utilizing a horizontal alignment film inone direction and a vertical alignment film in another, although arubbing process is required.

In the second basic configuration of the invention, since no transparentelectrode 112 is formed in the transmissive regions T, steps for formingtransparent electrodes 112 and barrier metal layers 136 can be omittedto reduce the manufacturing cost just as in the first basicconfiguration.

FIG. 4 shows a liquid crystal display according to a combination of thefirst and second basic configurations. As shown in FIG. 4, reflectiveelectrodes 20 a to 20 f are formed at intersections between bus lines 10and 12 and above TFTs 14. The reflective electrodes 20 a to 20 f haveopenings 37 a to 37 f that are formed in various configurations.

For example, the reflective electrode 20 a is formed with a plurality ofopenings 37 a constituted of V-shaped slits extending at an angle tolonger sides of the reflective electrodes 20 a. The reflective electrode20 b is formed with a plurality of triangular openings 37 b. Thereflective electrode 20 c is formed with a plurality of elongate rhombicopenings 37 c extending in parallel with shorter sides of the reflectiveelectrode 20 c. The reflective electrode 20 d is formed with a pluralityof hexagonal openings 37 d. The reflective electrode 20 e is formed witha plurality of straight openings 37 e extending in parallel with shortersides of the reflective electrode 20 e. The reflective electrode 20 f isformed with a plurality of straight openings 37 f extending in parallelwith shorter sides of the reflective electrode 20 f.

Like the first and second basic configurations, such a configurationalso makes it possible to omit the steps for forming transparentelectrodes 112 and barrier metal layers 136 for a reduced manufacturingcost.

Substrates for a liquid crystal display having the first and secondbasic configurations and liquid crystal displays having the same willnow be described with reference to first through seventh embodiments ofthe invention.

First, a liquid crystal display according to the first embodiment of theinvention will now be described with reference to FIGS. 5 and 6. Sincethe liquid crystal display of the present embodiment has a configurationsubstantially similar to the first basic configuration shown in FIGS. 1and 2, the description will be made with reference to FIGS. 1 and 2. Asshown in FIGS. 1 and 2, in the liquid crystal display of the presentembodiment, horizontal alignment films made of, for example, polyimideresin are formed on opposite surfaces of a TFT substrate 2 and anopposite substrate 4, and a predetermined rubbing process is performedon the same. The substrates 2 and 4 are combined with a cell gap d1 (of3 μm, for example) left therebetween, and a nematic liquid crystalhaving positive dielectric anisotropy (Δn=0.67) is sealed between thesubstrates 2 and 4. The alignment of the liquid crystal molecules is ahomogeneous alignment in which the major axes of the liquid crystalmolecules are in parallel with each other and also in parallel with thesubstrate surfaces.

A polarizer 32 is a circular polarization plate that is constituted of aλ/4 phase difference plate 39 provided on a glass substrate 26 and alinear polarization plate 38 provided outside the same. The polarizationaxis (light transmission axis) of the linear polarization plate 38 andthe optic axis (delay axis) of the λ/4 phase difference plate 39 areprovided at an angle of 45 degrees. The delay axis denotes the biggerone of the refractive index nx, ny toward inner surfaces of the opticalfilms. Similarly the polarization plate 34 is a circular polarizationplate that is constituted of a λ/4 phase difference plate 41 provided onside of the glass substrate 27 and a linear polarization plate 40outside it. Polarization axis of the linear polarization plate 40 andthe delay axis of λ/4 phase difference plate 41 are rotated and fixed atan angle of 45 degrees.

In the present embodiment, reflective electrodes 20 are provided atintersections between the bus lines 10 and 12 and on the TFTs 14 just asin the first basic configuration, which reduces the area of the buslines 10 and 12 exposed in the transmissive regions T and T′ to increasethe area of the transmissive regions T and T′ without reducing the areaof the reflective regions R and R′. That is, in the present embodiment,regions which have not been used as reflective regions nor transmissiveregions in a transflective liquid crystal display according to therelated art are used as the transmissive regions T and T′. This makes itpossible to improve transmission characteristics without degradingreflection characteristics.

A display operation of the liquid crystal display of the presentembodiment will now be described with reference to FIGS. 5A, 5B, 6A, and6B. FIGS. 5A, 5B, 6A, and 6B show states of display of predeterminedimages on the liquid crystal display of the present embodiment. FIGS. 5Aand 5B are microphotographs showing states of display of predeterminedimages on the liquid crystal display of the present embodiment that areenlarged with a relatively high magnification (about 30×). FIGS. 6A and6B are microphotographs of states of display of predetermined images onthe liquid crystal display of the present embodiment that are enlargedwith a relatively low magnification (about 15×). FIGS. 5A and 6A showstates of display in the reflective mode, and FIGS. 5B and 6B showstates of display in the transmissive mode. As shown in FIGS. 5A, 5B,6A, and 6B, the present embodiment allows display in the transmissivemode without sacrificing high display characteristics in the reflectivemode.

The polarizer 32 used in the present embodiment is a circular polarizerthat is a combination of a linear polarizing plate 38 and a λ/4 phasedifference plate 39. Display characteristics of a transmissive displaydepend on the film used as the λ/4 phase difference plate 39. Table 1shows differences in transmission characteristic depending on the λ/4phase difference plate 39 that forms a part of the polarizer 32 on thebacklight side. TABLE 1 White display Black display λ/4 phase difference(cd/m²) (cd/m²) CR plate 39 of polarizer 32 5.1 1.9 2.7 one ARTON filmPhase difference film 5.3 1.7 3.0 with reciprocal wavelength dispersalNo film (linear 6.1 1.2 5.0 polarizer 38 only)

As shown in Table 1, when a sheet of ARTON film is used as the λ/4 phasedifference plate 39 of the polarizer 32, it provides luminance of 5.1cd/m² for a white display and luminance of 1.9 cd/m² for a blackdisplay. It provides a contrast ratio (CR) of 2.7.

When a phase difference film with reciprocal wavelength dispersion isused as the λ/4 phase difference plate 39 of the polarizer 32, itprovides luminance of 5.3 cd/m² for a white display and luminance of 1.7cd/m² for a black display. It provides a contrast ratio of 3.0.

When only the linear polarizer 38 is used without the λ/4 phasedifference plate 39, it provides luminance of 6.1 cd/m² for a whitedisplay and luminance of 1.2 cd/m² for a black display. It provides acontrast ratio 5.0. In this case, however, since brightness and darknessin a display are inverted between the transmissive mode and thereflective mode, grayscale signals must be converted in synchronism withthe turning on of the backlight to achieve a desired display.

It is apparent from the above that the liquid crystal display of thepresent embodiment can achieve transmission characteristics sufficientfor use in a dark place, although it has a contrast ratio lower thanthat of a transmissive liquid crystal display.

A description will now be made with reference to FIGS. 7A to 11 on asubstrate for a liquid crystal display and a liquid crystal displayhaving the same according to a second embodiment of the invention. Sincethe liquid crystal display of the present embodiment has a configurationsubstantially similar to the second basic configuration shown in FIG. 3,the description will be made with reference to FIG. 3. As shown in FIG.3, in the present embodiment, reflective electrodes 20 a to 20 e thatconstitute reflective regions R are formed in regions defined by gatebus lines 10 and drain bus lines 12. The reflective electrodes 20 a to20 e have openings 36 a to 36 e formed in various configurations. Theregions where the openings 36 a to 36 e are formed constitutetransmissive regions T.

For example, horizontal alignment films made of polyimide resin areformed on surfaces of a TFT substrate 2 and an opposite substrate 4 (notshown in FIG. 3), and a predetermined rubbing process is performed onthe same. The substrates 2 and 4 are combined with a cell gap of 2 μmtherebetween for example, and a nematic liquid crystal having positivedielectric anisotropy is sealed between the substrates 2 and 4. Thealignment of the liquid crystal molecules is a homogeneous alignment inwhich the major axes of the liquid crystal molecules are in parallelwith each other and also in parallel with the substrate surfaces.

A description will now be made with reference to FIGS. 7A to 11D onprinciples behind operations of the liquid crystal display of thepresent embodiment that is in the normally white mode. First, aprinciple behind operations in the reflective mode will be described.FIGS. 7A and 7B schematically show a sectional configuration of theliquid crystal display of the present embodiment taken in a reflectiveregion R. FIG. 7A shows a white display (a bright state), and FIG. 7Bshows a black display (a dark state). A λ/4 phase difference plate 41 isprovided on a side of a liquid crystal layer 24 in the reflective regionR, the side facing toward a viewer (upward in the figure). A linearpolarizer 40 is provided closer to a viewer than is the λ/4 phasedifference plate 41. The linear polarizer 40 has a polarization axis ina direction in parallel with the plane of the drawing. A reflectiveelectrode 20 is provided on the side of the liquid crystal layer 24opposite to the viewer's side (facing downward in the figure).

FIG. 8 shows an arrangement of optical axes of optical films of theliquid crystal display of the present embodiment as viewed from theviewer's side. As shown in FIG. 8, an optical axis 44 of the λ/4 phasedifference plate 41 on the viewer's side is rotated counterclockwise at45 degrees relative to a polarization axis 42 of the linear polarizer 40on the viewer's side. A polarization axis 50 of the polarizer 38 on thebacklight unit side is rotated clockwise at 45 degrees relative to anoptical axis 48 of the λ/4 phase difference plate 39. Liquid crystalmolecules 60 are aligned in parallel with the substrate surfaces.

In FIGS. 7A and 7B, external light is represented by a linearlypolarized light beam L1 having a polarization direction in parallel withthe polarization axis 42 of the linear polarizer 40 and a linearlypolarized light beam L2 having a polarization direction which isorthogonal to the light beam L1 and which is perpendicular to the planeof the drawing. Retardation (Δn·d1) that occurs in the liquid crystallayer 24 in the reflective region R becomes λ/4 when the liquid crystalmolecules 60 are aligned in parallel with the substrate surfaces andbecomes zero when the liquid crystal molecules 60 are alignedperpendicularly to the substrate surfaces.

As shown in FIG. 7A, when external light enters the linear polarizer 40from the viewer's side, the light beam L2 is absorbed by the linearpolarizer 40, and only the light beam L1 is transmitted by the linearpolarizer 40. When the light beam L1 thereafter enters the λ/4 phasedifference plate 41 having the optical axis 44 that is rotatedcounterclockwise at 45 degrees to the polarization direction of the sameas viewed from the viewer's side, it becomes a light beam L3 that iscircularly polarized counterclockwise as viewed from the viewer's side.Next, the light beam L3 enters the liquid crystal layer 24. No voltageis applied to the liquid crystal molecules 60 in the liquid crystallayer 24, in which state they are aligned substantially in parallel withthe substrate surfaces. In this state, the liquid crystal molecules 60have refractive index anisotropy, which results in retardation of λ/4 inthe liquid crystal layer 24. As a result, the light beam L3 becomes alinearly polarized light beam L4 having a polarization direction inparallel with the plane of the drawing, is reflected by reflectiveelectrode 20 and enters the liquid crystal layer 24. Because ofretardation in the liquid crystal layer 24, the light beam L4 becomes alight beam L5 that is circularly polarized clockwise as viewed from theviewer's side. Then, the light beam L5 enters the λ/4 phase differenceplate 41 and becomes a linearly polarized light beam L6 which is inparallel with the plane of the drawing and which exits the λ/4 phasedifference plate 41. Since the light beam L6 has a polarization axis inparallel with the polarization axis 42 of the linear polarizer 40 itpasses through the linear polarizer 40 to exit the same toward theviewer, which results in a white display.

As shown in FIG. 7B, when external light enters the linear polarizer 40from the viewer's side, the light beam L2 is absorbed by the linearpolarizer 40, and only the light beam L1 is transmitted by the linearpolarizer 40. Then, the light beam L1 enters the λ/4 phase differenceplate 41 and becomes a light beam L3 that is circularly polarizedcounterclockwise as viewed from the viewer's side. Next, the light beamL3 enters the liquid crystal layer 24. A predetermined voltage isapplied to the liquid crystal molecules 60 in the liquid crystal layer24, in which state they are aligned substantially perpendicularly to thesubstrate surfaces. In this state, since the liquid crystal molecules 60have no refractive index anisotropy, there is substantially zeroretardation in the liquid crystal layer 24. Thus, the light beam L3enters the reflective electrode 20 while remaining in thecounterclockwise circularly polarized state as viewed from the viewer'sside. The light beam L3 remains in the counterclockwise circularlypolarized state as viewed from the viewer's side though it is reflectedby the reflective electrode 20 and becomes a light beam L7 to enter theliquid crystal layer 24 again. Since there is substantially zeroretardation in the liquid crystal layer 24, the light beam L7 enters theλ/4 phase difference plate 40 while remaining in the counterclockwisecircularly polarized state as viewed from the viewer's side. It thenbecomes a linearly polarized light beam L8 which is perpendicular to theplane of the drawing and which exits the λ/4 phase difference plate 40.The light beam L8 is absorbed by the linear polarizer 40 because it hasa polarization direction orthogonal to the polarization axis 42 of thelinear polarizer 40, and the light does not exit toward the viewer,which results in a black display.

A principle of operations in the transmissive mode will be described.FIGS. 9A and 9B schematically show a sectional configuration of theliquid crystal display of the present embodiment taken in a transmissiveregion T. FIG. 9A shows a white display, and FIG. 9B shows a blackdisplay. A λ/4 phase difference plate 39 is provided on a side of liquidcrystal layer 24 in the transmissive region T, the side facing toward abacklight unit (downward in the figure). A linear polarizer 38 isprovided closer to the backlight unit than is the λ/4 phase differenceplate 39.

Referring to FIG. 8 again, the optical axis 44 of the λ/4 phasedifference plate 41 on the viewer's side is rotated counterclockwise at45 degrees relative to the polarization axis 42 of the linear polarizer40 on the viewer's side. The polarization axis 50 of the polarizer 38 onthe backlight unit side is rotated clockwise at 45 degrees relative tothe optical axis 48 of the λ/4 phase difference plate 39.

In FIGS. 9A and 9B, illumination light from the backlight unit isrepresented by a linearly polarized light beam L11 having a polarizationdirection in parallel with the polarization axis 50 of the linearpolarizer 38 and a linearly polarized light beam L12 having apolarization direction which is orthogonal to the light beam L11.Retardation (Δn·d2) that occurs in the liquid crystal layer 24 in thetransmissive region T becomes λ/2 when the liquid crystal molecules 60are aligned in parallel with the substrate surfaces and becomessubstantially zero when the liquid crystal molecules 60 are alignedperpendicularly to the substrate surfaces.

As shown in FIG. 9A, when the illumination light from the backlight unitenters the linear polarizer 38, the light beam L12 is absorbed by thelinear polarizer 38, and only the light beam L11 is transmitted by thelinear polarizer 38. When the light beam L11 thereafter enters the λ/4phase difference plate 39 having the optical axis 48 that is rotatedcounterclockwise at 45 degrees to the polarization direction of the sameas viewed from the viewer's side, it becomes a light beam L13 that iscircularly polarized counterclockwise as viewed from the viewer's side.Next, the light beam L13 enters the liquid crystal layer 24. No voltageis applied to the liquid crystal molecules 60 in the liquid crystallayer 24, in which state they are aligned substantially in parallel withthe substrate surfaces. In this state, the liquid crystal molecules 60have refractive index anisotropy, which results in retardation of λ/2 inthe liquid crystal layer 24. As a result, the light beam L13 becomes aclockwise circularly polarized light beam L14 as viewed from theviewer's side. Then, the light beam L14 enters the λ/4 phase differenceplate 41 and becomes a linearly polarized light beam L15 in parallelwith the plane of the drawing to exit the λ/4 phase difference plate 41.Since the light beam L15 has a polarization direction in parallel withthe polarization axis 42 of the linear polarizer 40, it passes throughthe linear polarizer 40 to exit the same toward the viewer, whichresults in a white display.

As shown in FIG. 9B, when the illumination light from the backlight unitenters the linear polarizer 38, the light beam L12 is absorbed by thelinear polarizer 38, and only the light beam L11 is transmitted by thelinear polarizer 38. Then, the light beam L11 enters the λ/4 phasedifference plate 39 and becomes a counterclockwise circularly polarizedlight beam L16 as viewed from the viewer's side. Next, the light beamL16 enters the liquid crystal layer 24. A predetermined voltage isapplied to the liquid crystal molecules 60 in the liquid crystal layer24, in which state they are aligned substantially perpendicularly to thesubstrate surfaces. In this state, since the liquid crystal molecules 60have no refractive index anisotropy, there is substantially zeroretardation in the liquid crystal layer 24. Thus, the light beam L16exits the liquid crystal layer 24 while remaining in thecounterclockwise circularly polarized state as viewed from the viewer'sside. The light beam L16 enters the λ/4 phase difference plate 41 andbecomes a linearly polarized light beam L17 which is perpendicular tothe plane of the drawing and which exits the λ/4 phase difference plate41. The light beam L18 is absorbed by the linear polarizer 40 because ithas a polarization direction orthogonal to the polarization axis 42 ofthe linear polarizer 40, and the light does not exit toward the viewer,which results in a black display.

FIGS. 10A to 10D show states of display of the liquid crystal display ofthe present embodiment in the reflective mode, and FIGS. 11A to 11D showstates of display of the liquid crystal display of the presentembodiment in the transmissive mode. FIGS. 10A and 11A show states ofdisplay at a grayscale voltage of 0 V. FIGS. 10B and 11B show states ofdisplay at a grayscale voltage of 4.3 V. FIGS. 10C and 11C show statesof display at a grayscale voltage of 5 V. FIGS. 10D and 11D show statesof display at a grayscale voltage of 8 V.

As shown in FIG. 10A, the plurality of openings 36 are in the form of arhombus having a width of 36 μm and a height of 4 μm, for example.Intervals between openings 36 adjacent to each other in the horizontaldirection of the figure are 24 μm, and intervals between openings 36adjacent to each other in the vertical direction of the figure are 20μm.

As shown in FIGS. 10A to 10D, in the reflective mode, the liquid crystaldisplay of the present embodiment provides a white display at thegrayscale voltage of 0 V and provides darker displays as the grayscalevoltage increases. The liquid crystal display of the present embodimentprovides a black display at the grayscale voltage of 8 V. As shown inFIGS. 11A to 11D, in the transmissive mode, the liquid crystal displayof the present embodiment provides a white display at the grayscalevoltage of 0 V and provides darker displays as the grayscale voltageincreases. The liquid crystal display of the present embodiment providesa black display at the grayscale voltage of 8 V. Thus, the presentembodiment provides good display characteristics in both of thereflective and transmissive modes as shown in FIGS. 10A to 11D.

A description will now be made with reference to FIGS. 12 to 14D on asubstrate for a liquid crystal display and a liquid crystal displayhaving the same according to a third embodiment of the invention. Thepresent embodiment is different from the second embodiment in thatvertical alignment films made of polyimide resin, for example, areformed on surfaces of a TFT substrate 2 and an opposite substrate 4facing each other. The substrates 2 and 4 are combined with a cell gapof 3 μm therebetween for example, and a nematic liquid crystal havingnegative dielectric anisotropy (Δn=0.08; Δε=−4) is sealed between thesubstrates 2 and 4. The alignment of the liquid crystal molecules is ahomeotropic alignment in which the major axes of the liquid crystalmolecules are in parallel with each other and are perpendicular to thesubstrate surfaces.

FIG. 12 shows an arrangement of optical axes of optical films of theliquid crystal display of the present embodiment as viewed from theviewer's side. Unlike the second embodiment shown in FIG. 8, thealignment of liquid crystal molecules 60 is oriented in a directionperpendicular to the plane of the drawing when no voltage is appliedthereto. The arrangement of the optical axes of the optical films issimilar to that in the second embodiment.

FIGS. 13A to 13D show states of display of the normally black modeliquid crystal display of the present embodiment in the reflective mode,and FIGS. 14A to 14D show states of display of the normally black modeliquid crystal display of the present embodiment in the transmissivemode. FIGS. 13A and 14A show states of display at a grayscale voltage of0 V. FIGS. 13B and 14B show states of display at a grayscale voltage of4.3 V. FIGS. 13C and 14C show states of display at a grayscale voltageof 5 V. FIGS. 13D and 14D show states of display at a grayscale voltageof 8 V.

As shown in FIGS. 13A to 13D, in the reflective mode, the liquid crystaldisplay of the present embodiment provides a black display at thegrayscale voltage of 0 V and provides brighter displays as the grayscalevoltage increases. The liquid crystal display of the present embodimentprovides a white display at the grayscale voltage of 8 V. As shown inFIGS. 14A to 14D, in the transmissive mode, the liquid crystal displayof the present embodiment provides a black display at the grayscalevoltage of 0 V and provides brighter displays as the grayscale voltageincreases. The liquid crystal display of the present embodiment providesa white display at the grayscale voltage of 8 V. Thus, the presentembodiment provides good display characteristics in both of thereflective and transmissive modes as shown in FIGS. 13A to 14D.

A description will now be made with reference to FIGS. 15 to 17D on asubstrate for a liquid crystal display and a liquid crystal displayhaving the same according to a fourth embodiment of the invention. Theliquid crystal display of the present embodiment has a configurationsubstantially similar to that of the second embodiment except for theorientation of the alignment of liquid crystal molecules 60 and theshape of openings 36.

FIG. 15 shows an arrangement of optical axes of optical films of theliquid crystal display of the present embodiment as viewed from aviewer's side. Unlike the second embodiment shown in FIG. 8, thealignment of liquid crystal molecules 60 is oriented in a direction inparallel with a phase-delay axis 44 of a λ/4 phase difference plate 41when no grayscale voltage is applied thereto. The arrangement of theoptical axes of the optical films is similar to that in the secondembodiment.

FIGS. 16A to 16D show states of display of the normally white modeliquid crystal display of the present embodiment in the reflective mode,and FIGS. 17A to 17D show states of display of the normally white modeliquid crystal display of the present embodiment in the transmissivemode. FIGS. 16A and 17A show states of display at a grayscale voltage of0 V. FIGS. 16B and 17B show states of display at a grayscale voltage of4.3 V. FIGS. 16C and 17C show states of display at a grayscale voltageof 5 V. FIGS. 16D and 17D show states of display at a grayscale voltageof 8 V. As shown in FIG. 16A, the plurality of openings 36 are in theform of a rhombus having a width of 37 μm and a height of 5 μm, forexample. Intervals between openings 36 adjacent to each other in thehorizontal direction of the figure are 23 μm, and intervals betweenopenings 36 adjacent to each other in the vertical direction of thefigure are 5 μm.

As shown in FIGS. 16A to 16D, in the reflective mode, the liquid crystaldisplay of the present embodiment provides a white display at thegrayscale voltage of 0 V and provides darker displays as the grayscalevoltage increases. The liquid crystal display of the present embodimentprovides a black display at the grayscale voltage of 8 V. As shown inFIGS. 17A to 17D, in the transmissive mode, the liquid crystal displayof the present embodiment provides a white display at the grayscalevoltage of 0 V and provides darker displays as the grayscale voltageincreases. The liquid crystal display of the present embodiment providesa black display at the grayscale voltage of 8 V. Thus, the presentembodiment provides good display characteristics in both of thereflective and transmissive modes as shown in FIGS. 16A to 17D.

A description will now be made with reference to FIGS. 18 to 20D on asubstrate for a liquid crystal display and a liquid crystal displayhaving the same according to a fifth embodiment of the invention. Theliquid crystal display of the present embodiment has a configurationsubstantially similar to that of the fourth embodiment except for theshape of openings 36.

FIG. 18 shows an arrangement of optical axes of optical films of theliquid crystal display of the present embodiment as viewed from aviewer's side. The arrangement of the optical axes of the optical filmsis similar to that in the second embodiment.

FIGS. 19A to 19D show states of display of the normally white modeliquid crystal display of the present embodiment in the reflective mode,and FIGS. 20A to 20D show states of display of the normally white modeliquid crystal display of the present embodiment in the transmissivemode. FIGS. 19A and 20A show states of display at a grayscale voltage of0 V. FIGS. 19B and 20B show states of display at a grayscale voltage of4.3 V. FIGS. 19C and 20C show states of display at a grayscale voltageof 5 V. FIGS. 19D and 20D show states of display at a grayscale voltageof 8 V. As shown in FIG. 19A, the plurality of openings 36 are in theform of a rectangle having a width of 30 μm and a height of 6 μm, forexample. Intervals between openings 36 adjacent to each other in thehorizontal direction of the figure are 30 μm, and intervals betweenopenings 36 adjacent to each other in the vertical direction of thefigure are 25 μm.

As shown in FIGS. 19A to 19D, in the reflective mode, the liquid crystaldisplay of the present embodiment provides a white display at thegrayscale voltage of 0 V and provides darker displays as the grayscalevoltage increases. The liquid crystal display of the present embodimentprovides a black display at the grayscale voltage of 8 V. As shown inFIGS. 20A to 20D, in the transmissive mode, the liquid crystal displayof the present embodiment provides a white display at the grayscalevoltage of 0 V and provides darker displays as the grayscale voltageincreases. The liquid crystal display of the present embodiment providesa black display at the grayscale voltage of 8 V. Thus, the presentembodiment provides good display characteristics in both of thereflective and transmissive modes as shown in FIGS. 19A to 20D.

A description will now be made with reference to FIG. 21 on a substratefor a liquid crystal display and a liquid crystal display having thesame according to a sixth embodiment of the invention. As shown in FIG.21, the liquid crystal display of the present embodiment is an IPS(In-Plane Switching) mode liquid crystal display in which liquid crystalmolecules are driven by a transverse electric field. A comb-shapedreflective electrode 21 and a comb-shaped common electrode 31 facing thereflective electrode 21 are provided in each pixel region on a TFTsubstrate 2. The region where the reflective electrode 21 and the commonelectrode 31 are formed serves as a reflective region R, and the regionbetween the electrodes 21 and 31 serves as a transmissive region T.Alignment films formed on the TFT substrate 2 and an opposite substrate4 may be either horizontal alignment films or vertical alignment films.The present embodiment can provide advantages similar to those of thefirst embodiment.

A substrate for a liquid crystal display according to a seventhembodiment of the invention will now be described with reference toFIGS. 22A and 22B and FIG. 23. FIGS. 22A and 22B show a schematicconfiguration of the substrate for a liquid crystal display of thepresent embodiment. FIG. 22A shows a sectional configuration of a TFTsubstrate 2 of the present embodiment, and FIG. 22B shows the section ofthe TFT substrate 2 before the formation of openings 36.

As shown in FIG. 22A, a plurality of recesses and projections are formedon a surface of a planarization film 28. A reflective electrode 20 isformed on the planarization film 28. On a surface of the reflecting film20, recesses and projections are formed in association with the recessesand projections formed on the surface of the planarization film 28located under the same. A plurality of openings 36 are formed on thereflective electrode 20. The openings 36 are formed in substantiallyflat regions 72 as shown in FIG. 22B where the surface of the reflectiveelectrode 20 is at an average inclination of 5 degrees or less to thesubstrate surface.

FIG. 23 shows changes in reflectivity Y of the reflective electrode 20depending on an average inclination k. The abscissa axis represents theaverage inclination k (deg.) of the reflective electrode 20 relative tothe substrate surface, and the ordinate axis represents the reflectivityY (%) in a direction perpendicular to the substrate surface. Parallellight at incident angles of 0 deg., 15 degrees, 30 degrees, and 40degrees and diffuse light produced using an integrating sphere are usedas incident light.

As shown in FIG. 23, the greater the incident angle of parallel light,the greater the average inclination k that yields the maximumreflectivity Y. It is apparent that an average inclination k in a rangeof 5 degrees or less does not contribute to improvement of reflectioncharacteristics in an actual environment because light enters the liquidcrystal display in various directions in an actual environment of use.Therefore, transmission characteristics can be improved whilesuppressing reduction of reflection characteristics by forming theopenings 36 in the substantially flat regions 72 where the averageinclination k is 5 degrees or less. The present embodiment makes itpossible to provide a transflective liquid crystal display that utilizeslight with high efficiency.

A description will now be made with reference to FIGS. 24 to 26 on asubstrate for a liquid crystal display and a liquid crystal displayhaving the same according to an eighth embodiment of the invention. FIG.24 shows a sectional configuration of the substrate for a liquid crystaldisplay and the liquid crystal display having the same of the presentembodiment. FIG. 24 omits a planarization film 28 that makes a cell gapd1 in a reflective region R substantially equal to one-half of a cellgap d2 in a transmissive region T. As shown in FIG. 24, an oppositesubstrate 4 has a CF layer 70 on a glass substrate 27. The CF layer 70is formed such that it has a thickness in a transmissive region T thatis substantially twice the thickness of the same in a reflective regionR and is formed with different degrees of color purity. The presentembodiment provides improved display characteristics because there is nochromatic deviation between the reflective mode and transmissive mode.

FIG. 25 shows a modification of the substrate for a liquid crystaldisplay and the liquid crystal display having the same of the presentembodiment. FIG. 25 omits a planarization film 28 that makes a cell gapd1 in a reflective region R substantially equal to one-half of a cellgap d2 in a transmissive region T. As shown in FIG. 25, a TFT substrate2 has a CF layer 70 on a glass substrate 20. Since the surface of the CFlayer 70 is substantially flatly formed, the CF layer 70 is formed suchthat it is different in thickness between a reflective region R where areflective electrode 20 is formed and a transmissive region T where noreflective electrode 20 is formed. The present embodiment providesimproved display characteristics because there is no chromatic deviationbetween the reflective mode and transmissive mode.

FIG. 26 shows another modification of the substrate for a liquid crystaldisplay and the liquid crystal display having the same of the presentembodiment. FIG. 26 omits a planarization film 28 that makes a cell gapd1 in a reflective region R substantially equal to one-half of a cellgap d2 in a transmissive region T. As shown in FIG. 26, a thicknessadjusting film 74 for adjusting the thickness of a CF layer 70 inreflective regions R is formed under reflective electrodes 20. Forexample, the thickness adjusting film 74 is formed of the same materialas that of a protective film (not shown) for TFTs 14 at the same timewhen the latter is formed. Since the surface of the CF layer 70 issubstantially flatly formed, the CF layer 70 is formed such that it isdifferent in thickness between the reflective regions R and transmissiveregions T. The present embodiment provides improved displaycharacteristics because there is no chromatic deviation between thereflective mode and transmissive mode.

As described above, in the present mode for carrying out the invention,it is possible to provide a substrate for a liquid crystal display and aliquid crystal display having the same which achieve excellent displaycharacteristics at a low cost. Second Mode for Carrying Out theInvention

Second Mode for Carrying Out the Invention

A liquid crystal display in a second mode for carrying out the inventionwill now be described with reference to FIGS. 27 and 28. FIG. 27 shows aconfiguration of the liquid crystal display in the present mode forcarrying out the invention. Components having functions and effects likethose in the liquid crystal display in the first mode for carrying outthe invention are indicated by like reference numerals and will not bedescribed here. As shown in FIG. 27, reflective electrodes 20 a to 20 ethat constitute reflective regions of a transflective liquid crystaldisplay are formed in regions defined by gate bus lines 10 and drain buslines 12. The reflective electrodes 20 a, 20 b, 20 d, and 20 e arerespectively formed with openings 36 a, 36 b, 36 d, and 36 e formed invarious configurations such as slits and circular holes. Notches 36 a′to 36 e′ in various configurations such as slits and circular orpolygonal holes are formed at the periphery of the reflective electrodes20 a to 20 e, respectively.

For example, the reflective electrode 20 a is formed with one opening 36a in the form of a slit extending substantially in parallel with longersides of the reflective electrode 20 a and a plurality of notches 36 a′in the form of slits that are inwardly cut at the two longer sides ofthe reflecting electrode 20 a opposite to each other and that extend atan angle to the longer sides. The reflective electrode 20 b is formedwith a plurality of opening 36 b in the form of slits extendingsubstantially in parallel with shorter sides of the reflective electrode20 b and a plurality of notches 36 b′ in the form of slits that areinwardly cut at two longer sides of the reflecting electrode 20 b andthat extend substantially in parallel with the shorter sides thereof.The reflective electrode 20 c has a plurality of notches 36 c′ adjacentto each other in the form of wedges that are inwardly cut at two longersides of the reflective electrode 20 c and that extend substantially inparallel with shorter sides of the reflective electrode 20 c. Thereflective electrode 20 d is formed with a plurality of circularopenings 36 d and a plurality of circular notches 36 d′ that areinwardly cut at two longer sides and two shorter sides of the reflectingelectrode 20 d. The reflective electrode 20 e is formed with one opening36 e in the form of a slit extending substantially in parallel withlonger sides of the reflective electrode 20 e and a plurality of notches36 e′ in the form of wedges that are inwardly cut at two longer sides ofthe reflecting electrode 20 e and that extend substantially in parallelwith shorter sides of the reflective electrode 20 e.

The regions where the reflective electrodes 20 a to 20 e are formedserve as reflective regions. The regions where the openings 36 a, 36 b,36 d, and 36 e and the regions at the periphery of the reflectiveelectrodes 20 a to 20 e where the notches 36 a′ to 36 e′ are formedserve as transmissive regions. No transparent electrode is formed at theopenings 36 a, 36 b, 36 d, and 36 e and the notches 36 a′ to 36 e′.Liquid crystal molecules in the transmissive regions are driven by anoblique field that is present between edges of the reflective electrodes20 a to 20 e and a common electrode 52 (not shown in FIG. 27) at theopposite substrate 4 substantially similarly to liquid crystal moleculesin the respective reflective regions at the same pixels.

While the openings 36 a, 36 b, 36 d, and 36 e and the notches 36 a′ to36 e′ in FIG. 27 are formed in configurations that vary from pixel topixel, the openings 36 a, 36 b, 36 d, and 36 e and the notches 36 a′ to36 e′ may be formed in the same configuration in the respective pixels.The openings 36 a, 36 b, 36 d, and 36 e and the notches 36 a′ to 36 e′may have a configuration to regulate alignment of liquid crystalmolecules. As a result, in a VA (Vertical Aligned) mode liquid crystaldisplay in which liquid crystal molecules are aligned substantiallyperpendicularly to the substrate surface, separate alignments can beachieved without a process of rubbing the alignment film. The presentmode for carrying out the invention may be applied to a liquid crystaldisplay in the TN mode utilizing a horizontal alignment film or the HAN(Hybrid Aligned Nematic) mode utilizing a horizontal alignment film inone direction and a vertical alignment film in another, although arubbing process is required. In the present mode for carrying out theinvention, it is possible to achieve transmission characteristics higherthan those of a transflective liquid crystal display in the related art.

FIG. 28 shows a modification of the configuration of the liquid crystaldisplay in the present mode for carrying out the invention. As shown inFIG. 28, reflective electrodes 20 f to 20 k are formed at intersectionsbetween bus lines 10 and 12 and above TFTs 14. Openings 36 i and notches36 f′ to 36 k′ having various configurations are formed at thereflective electrodes 20 f to 20 k.

For example, the reflective electrode 20 f is formed with a plurality ofnotches 36 f′ that are inwardly cut at two longer sides and one shorterside of the reflective electrode 20 f and that extend at an angle to thelonger sides of the reflective electrode 20 f. The reflective electrode20 g is formed with a plurality of triangular notches 36 g′ that areinwardly cut at two longer sides of the reflective electrode 20 g. Thereflective electrode 20 h is formed with a plurality of notches 36 h′adjacent to each other in the form of wedges that are inwardly cut attwo longer sides of the reflective electrode 20 h and that extendsubstantially in parallel with shorter sides of the reflective electrode20 h. The reflective electrode 20 i is formed with a plurality ofhexagonal openings 36 i and a plurality of hexagonal notches 36 i′ thatare inwardly cut at two longer sides of the reflecting electrode 20 i.The reflective electrode 20 j is formed with a plurality of notches 36j′ in the form of slits that are inwardly cut at a shorter side of thereflective electrode 20 j and that extend substantially in parallel withlonger sides of the reflective electrode 20 j. The reflective electrode20 k is formed with a plurality of notches 36 k′ in the form of slitsthat are inwardly cut at two longer sides of the reflective electrode 20k and that extend substantially in parallel with shorter sides of thereflective electrode 20 k. The ends of the notches 36 k′ are circularlyrounded.

The regions where the reflective electrodes 20 f to 20 k are formedserve as reflective regions. The regions where the openings 36 i areformed, the regions at the periphery of the reflective electrodes 20 fto 20 k where the notches 36 f′ to 36 k′ are formed, and the regionsaround the reflective electrodes 20 f to 20 k serve as transmissiveregions. The present modification makes it possible to achievetransmission characteristics higher than those of a transflective liquidcrystal display in the related art.

The invention is not limited to the above-described modes for carryingout the same, and various modifications are possible. For example, whilelight scattering characteristics are improved by recesses andprojections formed on the surface of the reflective electrodes 20 in theabove-described modes for carrying out the invention, the invention isnot limited to the same. Light scattering characteristics may beimproved by forming the reflective electrodes 20 may be formed with aflat surface (mirror surface) and by providing a forward scatteringplate on the opposite substrate 4 on the viewer's side.

As described above, the invention makes it possible to provide asubstrate for a liquid crystal display and a liquid crystal displayhaving the same which achieve excellent display characteristics at a lowcost.

1-15. (canceled)
 16. A substrate for a liquid crystal displaycomprising: a base substrate that sandwiches a liquid crystal incombination with a counter substrate provided counter thereto; aplurality of bus lines formed on the base substrate such that theyintersect with each other with an insulation film interposedtherebetween; thin film transistors formed in the vicinity of positionswhere the plurality of bus lines intersect with each other; and aplurality of pixel regions constituted of a plurality of reflectiveregions in which reflective electrodes for reflecting incident lightfrom the side of the top surface of the base substrate are formed in theform of a matrix and transmissive regions which are formed by providingopenings in the reflective regions and which transmit incident lightfrom the side of a bottom surface of the base substrate toward the topsurface of the base substrate, wherein the openings have a configurationto regulate alignment of liquid crystal molecules.
 17. A substrate forliquid crystal display according to claim 16, wherein the openingsgenerate an oblique field for regulating the alignment of the liquidcrystal molecules at a voltage applied.
 18. A liquid crystal displayhaving a pair of substrates and a liquid crystal sealed between the pairof substrates, wherein a substrate for a liquid crystal displayaccording to claim 16 is used as either of the substrates.
 19. A liquidcrystal display having a pair of substrates and a liquid crystal sealedbetween the pair of substrates, wherein a substrate for a liquid crystaldisplay according to claim 17 is used as either of the substrates.
 20. Aliquid crystal display according to claim 18, wherein the liquid crystalmolecules are aligned substantially perpendicularly to the substratesurface at no voltage applied.
 21. A liquid crystal display according toclaim 19, wherein the liquid crystal molecules are aligned substantiallyperpendicular to the substrate surface at no voltage applied.